Control of centrifugal fans, pumps, and the like



Dec. 13, 1938. I I M 2,140,148

CONTROL OF'GENTRIFUGAL FANS, PUMPS, AND THE LIKE Filed Oct. 14, 1956 :5Sheets-Sheet 1 Dec. 13, 1938. q, HITMORE 2,140,148

CONTROL OF CENTRIFUGAL FANS, PUMPS, AND THE LIKE Filed Oct. 14, 1936 sSheets-Sheet 2 Dec. 13, 1938. J w g 2,140,148

CONTROL OF CENTRIFUGAL FANS, PUMPS, AND THE LIKE Filed Oct. 14, .1936 ssheets-sheets 15 F1911. Z0 A- 7 fi'zgw 20 10 f 6 I I I 27 I I 25 5Patented Dec. 13, 1938 PATENT OFFlCE CONTROL OF CENTRIFUGAL FANS, PUMPS,AND THE LIKE John Whitmore, Belfast, Ireland, assignor to Davidson &Company, Limited, Belfast, Ireland Application October 14, 1936, SerialNo. 105,484 In Great Britain October 30, 1935 20 Claims. (Cl. 230-114)This invention relates to the control of the performance of centrifugalfans, pumps and the like (hereinafter referred to as a centrifugal fan)and is more particularly applicable, but not limited to such units whenarranged to operate at constant speed.

The object of the invention is to maintain the efficiency of theapparatus when running for example at constant speed on partial loads,by a saving of the power required to operate the impeller of the fan atsuch decreased loads.

Hitherto in centrifugal fans in which the entering air is given avortical motion at entry for the purpose of obtaining economy inoperation, the volume of air corresponding to the full load on the fanflows over movable or stationary guide vanes, or their equivalent, Suchvanes are usually placed in or near the fan inlet or within the fancasing, in such position that the air has to pass over such vanes toproduce the desired vortical movement and are, consequently, more orless of an obstruction under all operating conditions. This isparticularly undesirable when the fan is operating on full load, as itfrequently results that to meet a stated performance, it is foundnecessary to resort to an increase in the fan size, compared with thesize of fan having an inlet free of vanes or obstructions of any kind.

' The object of the invention is to provide a centrifugal fan, capableof being operated with efficiency at loads less than maximum, and at thesame time to provide a fan in which the eye or axial inlet thereof isunrestricted when i the fan is operating at full load, that is to say,

a fan wherein the whole of the entering air under maximum load passesdirectly to the impeller without the impediment of vanes or otherdevices for creating a vortical movement in the entering air.

According to the invention a method of regulating a centrifugal fan atall loads less than the maximum consists in causing the volume of airaxially approaching the fan to flow into the fan in at least twocontrollable portions one of which passes through the eye of the fan andconstitutes a main or axial inlet (hereinafter termed the main inlet)and the other through a secondary inlet, which latter, when open, givesthe air passing therethrough. a flow in the direction of rotation of theimpeller and is adapted to impart a similar flow to the air streamflowing through the main inlet when the latter is open.

Preferably the flow of air through both inlets is controlledsimultaneously, in some cases a damper being disposed in the fandischarge, whereby additional control may be effected for example whenthe secondary air inlet alone'is open.

Further, according to the invention there is provided a centrifugal fanhaving associated therewith mechanism which at all loads less than themaximum causes the volume of air axially approaching the fan to howthereinto in at least two controllable portions one of which constitutesa main air supply (hereinafter termed the main air) and the other asecondary air supply (hereinafter termed the secondary air) whichlatter, when admitted, flows over vanes which give such secondary air aflow in the direction of rotation of the impeller and thereby impartinga similar flow to the main air stream when the latter is admitted.

The admission of main and secondary air streams is preferably controlledsimultaneously by dampers or their equivalent (hereinafter referred toas dampers) and the air flowing through the fan discharge may becontrolled by a damper for example when the secondary air only isadmitted.

In a suitable construction according to the invention a centrifugal fanis provided with dampers which are used to control the supply of airthrough the main inlet of the fan, the dampers being capable ofsimultaneously opening a secondary inlet to the fan through which airmay enter and flow over vanes, blades or the like (hereinafter termedvanes) which give said entering air a directional movement correspondingto the line of rotation of the impeller. The arrangement is such thatwhen the main inlet of the fanis partially closed by the dampers air ispermitted to enter the secondary inlet, flow over the vanes and impingeupon or contact with the-in-flowing stream of air passing through themain inlet, whereby a similar motion is imparted to such stream in adirection corresponding to the line of rotation of the impeller. Thedampers are operated by mechanism which enables them to be used to closeor partially close the main inlet and simultaneously open fully or inpart the secondary air inlet. The dampers may, however, be so formedthat when the main inlet of the fan is totally closed the secondary airinlets may also be completely closed.

Preferably in one embodiment of the invention the outlet of the fan isprovided with the usual form of damper which is operated to stillfurther control the output of the fan especially when the main inlet ofthe fan is totally closed and air to the impeller is flowing through thesecondary inlet only.

In order that the invention may be clearly understood reference isdirected to the accorn panying drawings wherein:

Figure 1 shows a side elevation of the fan casing with the dampers andcontrol gear therefor in part section.

Figure 2 is a front elevation of Figure 1 looking towards the fanoutlet, the upper portion being a section on lines A-A Figure 1.

Figure 3 illustrates in detail and to a larger scale part of a damperactuating screw rod hav ing two different pitches of thread.

Figures 4 and 5 show sectional elevations of alternative arrangement ofvanes.

Figures 6, 7 and 14 illustrate further alternative methods of operatingthe dampers.

Figures 8, 9, 10 and 11 and 12 and 13, illustrate respectively in frontand side elevation dampers of modified form.

The same distinguishing numbers are used for the same parts throughoutthe drawings.

In carrying the invention into effect in one convenient mannenand withparticular reference to Figures 1 and 2, l indicates a fan casing, 2 animpeller within said casing and carried by a rotary shaft 3, 4 is atangential outlet from the casing, and 5 is the main inlet thereto,which may be fitted with a flaring 26. .A system of stationary vanes 6is arranged around the main inlet 5 of the fan which is surrounded by acylindrical casing 1 and forms an annular chamber 8 external to thesystem of vanes 6 which connect such chamber to the main inlet 5.

The stationary vanes 6 are so disposed that air, passing through themfrom the annular chamber 8 and forming a secondary air inlet to theimpeller 2 enters the impeller in a tangential direction (i. e. with avortical flow), a whirling or secondary motion or movement being therebyset up in the air entering the impeller through the main inlet of thefan i. e., the eye of the fan, the direction of whirl being the same asthe direction of rotation of the impeller.

Two pairs of oppositely moving dampers 9 slidably carried in guides l0,and operated by a right and left hand screw threaded rod ll, carried inbearings Ha are arranged to vary the effective area of the main inlet 5to the fan.

Each damper 9 in this construction comprises two plates, preferablyhaving concave inner edges and being of substantially crescent shapethus forming a compound damper, one plate of each pair of which movesrelatively faster than the other. To produce such relative travel rightand left hand threads of different pitches are formed on the rod I iwhich has a screw engagement with nuts [2 attached to each damper plate,one end of the screwed rod II extends outside the casing and carries acrank l3 by which the rod is turned to operate the dampers. Oppositelymoving dampers each comprising a single plate will be described later,but the arrangement now indicated possesses the great advantage that thecasing I can be made neat and compact, and therefore occupies arelatively small space.

When the fan or pump is operating at its full capacity, it is usuallyadvisable to close 01f the annular chamber 8 (formed by the interior ofthe casing 1 and the exterior of the vane system 6) to the passage ofair. This may be effected by shaping the outer ends of the dampers 9,Figcylindrical casing I.

ure 1, to fit (i. e. to the same curvature as) the interior of thecasing I and by covering the diametrically opposite segmental openingsformed by the upper and lower edges of the damper slides l0, and theinterior of the aforesaid casing, with correspondingly shaped shields 20so that air may only enter the fan in an axial direction. When compositedampers are fitted, that is where each damper blade comprises two ormore plates, it is advisable to make the outer edges of the oppositelysituated and quicker moving damper blades, that is, those which areactuated by the coarsest pitch, or quickest moving gear, if some otherform of actuating gear is employed of the same shape as the interior ofthe casing I, in order that the closure of the annular chamber 8 may beeffected by this portion of the dampers.

One of the guide vanes 6 (indicated by the reference 2!) atdiametrically opposite positions, Fig. 1, behind the shield 20, may beextended if desired across the annular chamber 8 to the interior face ofthe cylindrical casing "I, in order to prevent eddying in the aircurrent passing behind the said shields when annular passage 8 is open,which eddying might take place if air were to flow in oppositedirections.

Under certain circumstances it may be considered necessary to carry eachvane in the system of vanes 6 across the annular chamber 8. In thiscase, however, neither the segmental pieces '20 nor the curved shields25 (hereinafter mentioned) would be used.

Figure 3 shows on a larger scale one side of the right and left handscrew threaded rod H, one part of which is provided with a thread ofdifferent pitch to the other (in this case the,

right hand thread is about half the pitch of the other portion). Thenuts I2 may be attached to the dampers 9 in any approved manner. In theillustration each nut consists of a non-rotatable central portion ofanti-friction or other suitable metal screwed to suit the threads on therod H and carried between two brackets or snugs 12a welded or otherwisesecured to the dampers, or where necessary to extended portions of saiddampers. This construction is simple and effective, but may be varied tosuit circumstances. Housings 29 are shown in Figure 1 to accommodatesuch extensions and nuts, and also bearings Ila for the screwed rod H.

In Figure 4 the system of stationary vanes 6 is shown mounted in theinterior of fan casing l communicating respectively with the annularchamber 8 and the main inlet 5 to the impeller 2. A flange is formed onthe circular casing 1 in order that such casing may be convenientlyconnected to a duct or trunk l5 as shown in dotted lines.

Figure 5 illustrates another arrangement or modification in which thesystem of stationary vanes 6 projects at an angle into the fan casing I,while the inlet side of the vanes is external to the fan casing, and, asin Figure 1 communication is established between the annular space orchamber 8 and main inlet 5 by means of the vanes 6.

Figure 6 shows an alternative method for operating the dampers, themechanism being entirely external and consisting of a screwed rod l Icarried in bearings l6 and provided with right and left hand threadsoperating in nuts l2 which engage with levers l8 and [8A pivoted at 19and MA on brackets ll situated on each side of The ends of the leversremote from the nuts are coupled to extensions from the compositedampers and actuate same as already described. It will be observed thatthe double armed lever 58A derives its motion from double armed lever 58whereby one damper of each set travels faster than the other.

In this particular construction the fan shaft 3 projects through thevane and damper system without fouling the operating ear. The brackets51 may be attached to the circular casing I, or to any other part of thefan as found most convenient.

Figure '7 shows another form of damper actuating mechanism whichcomprises two pulleys, one of which may be operated by worm gear (notshown) or in any other manner, and mounted diametrically opposite eachother on brackets I! attached to the casing l or other convenient partof the fan. The pulleys carry endless ropes or chains 23, 23A or thelike which are attached to the dampers at 24. The method is shownapplied to composite or compound dampers and in this case each of thepulleys 22 consists of a double stepped cone, the larger step actuatingthefaster moving parts of eachcomposite damper plate, and the smallerone the slower moving parts. It will be readily understood that as theright hand pulley, for example, is rotated by hand or power in aclockwise direction, the ropes or the like 23A in each case will notonly drag the dampers 9 to which they are attached, with them, but thepulley on the opposite side will also be rotated, and in the same mannerwill traverse the dampers to which the ropes 23 are attached. Thus theratio of the diameters of the pulleys determines the relative speed foreach plate of the composite dampers. This particular arrangement has thefurther important advantage'that each damper plate may be balanced byits oppositely moving counterpart if the dampers are arranged to slidevertically. This condition can be visualized by turning Fig. '7 through90.

Under normal conditions of working, it is not necessary to entirelyprevent fiow of air through the vanes when the main' inlet is fullyclosed (that is when all main air flow is stopped) as the maximum flowof air which can flow freely through the vane system is small comparedwith the normal volume passing. Nevertheless, such secondary air fiowmay be completely prevented if desired, by the adoption of the followingalternative means:

A damper 84 may be provided in the fan outlet 4, Figure 1, to give asmall additional degree of volume regulation with economy, and will alsoserve to isolate the fan if required. Further, dampers of suitable shapemay be provided to control the passage of air into the annular chamber8, and may consist of semi-circular shields adapted to fit over theouter surface of the ring of vanes, or the flow of secondary air intothe annular chamber may be controlled by semi-circular shields adaptedto cover this space. For convenience of working the dampers controllingthe flow of air in the vane system, or into the annular chamber may bemounted on the sliding dampers controlling the flow into the axial inlet5. Such means as are now described in relation to Figures 8 and 9 willthereby enable the fan to deal with volumes of air approaching zero.

In this construction each damper 9 consists of a single plate only andin order to reduce the volume of air at low duties curved shields 25 arecarried on extensions from the outer ends of the dampers. These shieldsmay partially or wholly close the outer periphery of the vane systemwhen main air flow is stopped (as shown the shields 25 partially enclosethe vanes) that is, when the dampers 9 are closed and thus allow only avolume approaching zero to enter the fan. When the dampers 9 are in thefull open position, that is, when maximum flow is taking place, theshields 25 are accommodated in recesses 21 as shown dotted at the lefthand side of Figure 8.

Figures 10 and 11 are similar to Figures 8 and 9 and show an alternativeform of shield 25, in combination with the segmental covers 20 by meansof which it is possible to entirely close off all ingress of air throughthe system of vanes by means of extensions or ears 28, attached to orforming part of the ends of the curved shields 25. These extensions,when the dampers 9 are in the closed position to prevent flow of airthrough the main inlet, close the secondary inlet to the space behindthe segments 20 so that there is no flow of air whatever through theannular chamber 8. It will be understood that a similar form of shieldprovided with ears 28, may be fitted to a plain single type of damper,as illustrated in Figures 8 and. 9, together with the segmental portions20 referred to.

Figures 12 and 13 illustrate another method by which ingress to theannular chamber 8 may be entirely closed off when main air flow to theinlet 5 is stopped, thus also bringing the performance of the fan downto zero, or at least to the irreducible minimum. This is achieved byattaching to each damper 9, if only two are employed, or to one pair ofoppositely moving dampers if multiple damper plates are used, curvedshields 9A. These are accommodated in recesses 21 as before describedwhen the fan is working at maximum output. It will be understood thatany of the forms or arrangements of dampers may be fitted with theseveral forms of shields referred to or the methods of operating samemay be varied as required, for-instance the dampers shown in Figures 8and 9 could be fitted to the construction of fan shown in Figures 1 and2 and operated in accordance with the method described in connectionwith the construction shown in Figure '7.

The method of actuating the dampers by means of a right and left handthreaded rod having screws of different pitch is also illustrated inFigure 14 in which instance the threaded portion is shown external tothe cylindrical casing I, so that the nuts l2, and the screwed portionof. the rod, are not exposed to the action of gases, should the fan bedealing therewith, particularly if the temperature is considerable, orif the ingoing, air carries dust in suspension which would cause thescrews and threads to wear.

In cases where it is desired to employ screws for operating the damperswhen the driving shaft 3 passes through the axial inlet 5, two screwedrods (not shown) one on each side of the shaft may be employed, the onebeing actuated manually or otherwise and the other being driven from thefirst by a chain or sprocket gear or in any other approved manner.

It will be appreciated that the several methods described for operatingthe dampers are only representative of some mechanical devices which maybe used for this purpose, and it is not thought necessary to illustratefurther examples as the gear in question is only a matter of ordinaryengineering expedience and to some extent dependent upon existingconditions.

The apparatus operates in the following man+ ner:

when the fan is operating under full load, the

dampers 9, (Figure 1) will be open to their fullest extent, closing offall flow through the annular chamber 8, and the vane system 6, and thewhole ofthe' air or gas will then .flow directly to the impeller throughthe main inlet 5. When, however, the fan is required to operate on areduced or partial load the dampers 9 are moved towards each other, bymeans of the threaded rod II or other form of gear, consequently leavinga space between the outer ends of the said dampers and the casing I forair to enter the secondary inlet and vane system 6, which after passingtherethrough joins the main air flowing through the fan, impartingthereto a motion in the direction of rotation of the impeller with theresult that a reduction in power expenditure is efiected.

' It will be understood that as the proportion of air-flowing throughthe vane system 6 increases, thefvolume :of main air will decrease andif the dampers 9"are entirely closed, the whole of the air passingthrough the fan will in this case enter through the vane system, unlessthe vane system'iswentirely closed off as provided for.

But as already explained the quantity of air dealt with in comparisonwith the volume under normal conditions is small and may be reduced tozero in the manner and 'by-the means already described andxillustrated.I Various types of dampers maybe employed for controlling the passage ofair through the fan inlets; Furthermore, the damper employed for saidpurpose may be either a single-piece damper or a "damper consisting ofseveral co-acting damper elements. The term damper is, therefore,employed in the appended claims to cover various types of dampers andalso to cover a damper consisting of a single damper element or aplurality of co-ac'ti-ng damper elements, except as otherwisespecifically set forth.

The term air is employed in this specification and in the accompanyingclaims as referring to any matter which'may be conveyed or otherwisehandled through the medium of fans or the like.

It will also 'be understood that the fan may be connected through thecasing l to a flue or the like, and discharge freely to the atmosphere,or the outlet may be connected to 'a system-of trunking or the like,whilst the inlets draw freely from the atmosphere. In other cases boththe inlets and the outlet of the fan may be connected to fines or ducts,

What I cla-imand desire to secure by Letters Patent is:-

l. .A centrifugal fan or the like comprising an impeller, a main :airinlet adapted to pass a main air supply axially toward the impeller, asecondary'inle't adapted to pass a secondary air supply substantiallytangentially into a peripheral area withinsaid main air inletat a pointremoved from the impeller whereby to impart vertical movement to the,said main ai-r supplyinadesired direction prior to said main air.su-pplys entry into the impeller.

2. A centrifugal fan :or the like. according to claimv l, saidinletshaving co-related means for varying the relative passage of air'therethrough.

3. A centrifugal fan or the like according to claim 1, said :inle'tshaving co-related means for simultaneously varying the relative passageof air th'erethrough. V

4. A centrifugal tan or the like according to claim 1, said inletshaving co-related means for inversely modifying the passage-af airtherethrough. I l

, claim 1, the secondary inlet being disposed about the main inlet andadapted to pass a vortical air current tangentially into the main airsupply whereby to impart vertical movement thereto in a desireddirection.

7. A centrifugal fan or the like according to claim 1', the secondaryinlet comprising an annular chamber disposed about the main inlet and 'aplurality of passages extending inwardly therefrom tangentially into themain inlet.

8. A centrifugal fan or the like according to claim 1, the secondaryinlet comprising an annular chamber having an opening extending aboutthe main inlet, a passage extending inwardly from'the said chamber intothe main inlet, and vanes in said passage arranged substantiallytangentially relatively to the main inlet, said vanes being adapted :tocause the secondary air V supply to vort-i'ca-lly flow into the mainairsupply.

9.'A centrifugal fan or the like according to claim 1, said inletshaving adjacent openings, in a substantially common plane, for admittingair thereinto, and a movable damper having portions adapted to be movedacross said openings and to vary the passage of air into said inlets.

10; A centrifugal fan or the like comprising an impeller, a compoundinlet for passing air thereto, a main inlet opening, a secondary inletopening disposed about :said former. opening, and means for regulatingthe passage of air through said openings, the said means comprisingmovable damper elements adapted to be simultaneously moved, in oppositedirections, across said openings whereby to vary the efiective areasthereof. 7

11. A centrifugal fan or the like according to claim 10, the saidregulating means comprising simultaneously movable pairs of damperelements, one element of each pair being movable relatively faster thanthe other element thereof, the several elements of each of said pairsbeing adapted at outer positions to substantially overlap and form arestriction upon opposite portions of the secondary inlet opening and atinner positions to collectively form a substantial restriction upon themain inlet opening.

.12. Al -centrifugal fan or the like according to claim 10, the saiddamper elements havingportions extend over and substantially close bothsaid openings when .said portions are at an inner position.

13. Acentrifugal fan or the like according to claim 10, further having amechanism for actuating said d'amp'er elements.

1.4. A centrifugal fan or the like according to claim 10, further havinga mechanism for actuating said damper elements, comprising a rotatable"rod, oppositely threaded toward opposite ends thereof, and adapted toco-act with threaded portions on opposed damper elements whereby tosimultaneously move the latter towards or away from each other.

'15. A centrifugal fan'or the like according to claim 10, further havinga. mechanism for actuating said damper elements, comprising an endlesspulley line having oppositely movable portlons connected to opposeddamper elements.

16. A centrifugal fan or the like according to claim 10, furthercharacterized in having pairs of damper elements adapted to besimultaneously moved in opposite directions, one element of each pairbeing movable relatively faster than the other element thereof, and alsoin having a mechanism, for actuating said damper elements, comprising arotatable rod having portions toward each end thereof with threads ofdifferent pitch, each of said portions being adapted to co-act withdifierent damper elements whereby to impart difierent speeds of movementthereto.

17. A centrifugal fan or the like according to claim 10, furthercharacterized in having pairs of damper elements adapted to besimultaneously moved in opposite directions, one element of each pairbeing movable relatively faster than the other element thereof, and alsoin having a mechanism, for actuating said damper elements, comprising arotatable rod having oppositely threaded portions toward each endthereof, and levers, coacting with said threaded portions and withdifferent damper elements and adapted to impart different speeds ofmovement thereto.

18. A centrifugal fan or the like according to claim 10, furthercharacterized in having pairs of damper elements adapted to besimultaneously moved in opposite directions, one element of each pairbeing movable relatively faster than the other element thereof, and alsoin having a mechanism, for actuating said damper elements, comprisingtwo endless pulley lines, movable at difierent lineal speeds, each linehaving oppositely movable portions connected to opposed damper elements.

19. A centrifugal fan or the like comprising an impeller, an axial inletadapted to pass air substantially axially toward said impeller, anannular chamber substantially surrounding said axial inlet and adaptedto receive an air supply, an annular passage between said chamber andthe axial inlet, one or more vanes in said passage adapted to form oneor more nozzles to guide air from said chamber tangentially into theaxial inlet whereby to establish a vortical movement, in a desireddirection, in the axially flowing air passing therethrough, and a dampercomprising oppositely movable damper elements, adapted to vary thepassage of air through said annular passage and said axial inlet, thedamper having portions adapted to substantially close the said annularpassage and the said axial inlet when the damper elements are in aninner position.

20. A centrifugal fan or the like comprising an impeller, an axial inletadapted to pass air substantially axially toward said impeller, anannular chamber substantially surrounding said axial inlet and adaptedto receive an air supply, an annular passage between said chamber andthe axial inlet, one or more vanes in said passage adapted to form oneor more nozzles to guide air from said chamber tangentially into theaxial inlet whereby to establish a vortical movement, in a desireddirection, in the air passing therethrough, and one or more of saidvanes extending into the annular chamber whereby to minimize eddycurrents therein.

JOHN WHI'I'IVIORE'.

